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idle surge

Have a dramatic RPM surge going on at specific engine temps as the car warms up.

COLD ENGINE: no problem; idle correct, smooth

WARM ENGINE: ICV will suddenly (and i mean SUDDENLY!) open so that the idle in neutral jumps from 500 to 1300. If in D, stopped at a light, risk of suddenly jumping into the car in front. Idle will stay high for a minute or 2, then slowly go back down to 500. Problem may repeat as engine warms further.

Re: You can't test a MAF by measuring resistance...

I tried reading out the error codes - this is an old OBD1 car, so it's donw thru flashing idiot lights (short & long pulses).

All that came out, over and over, was a failed Lambda A. I've not yet reeplaced that but will. The same code just kept repeating, endlessly - either it's stored a zillion of these same coeds, or the memory is stuck, or it simply repeats until it is told to stop.

You may need to get codes read by a BMW computer

I assume that the full-blown BMW diagnostics computer will read more codes than the Stomp Test. But, I don't know personally, because I have not worked on a 1995 E38 like this before.

Try disconnecting the MAF and driving the car. If the symptom goes away or changes substantially, that might point to a bad MAF. Driving with the MAF unplugged will throw a check engine error, but you can always reset it after the test.2000 E38 750iL Highline Edition with 18" Style 118 Wheels and Runflats
MKIV and 16:9 Navigation, TV, and Backup Camera
New Gen Radio, Sirius, Aux Input for my iPod, Bluetooth, and E39 M5 Tire Pressure Monitor System

The idle surge could be ICV if dirty...

BTW... what year is the car, model, engine and production date because the problem could be a faulty CPS, if it is aftermarket instead of OE or OEM... most aftermarket are faulty because are technology copies with incomplete circuits...

Re: The idle surge could be ICV if dirty...

Nah -= it's clean.

THAT'S why I checked the voltages driving the ICV - to see if the voltages were changing without a reason.

And - see my list of voltages. For some reason the computer suddenly drove the ICV wide open - for a short time - then drifted back to normal. The ICV reacted as it should - opening up and then closing gradually as the voltages in Pins 1 & 3 returned to normal.

Probably time to connect to a BMW diagnostics comp

It is probably time to connect the car to a BMW diagnostics computer. Without the detail engine diagnostics codes, it is near impossible to figure out what is going on.2000 E38 750iL Highline Edition with 18" Style 118 Wheels and Runflats
MKIV and 16:9 Navigation, TV, and Backup Camera
New Gen Radio, Sirius, Aux Input for my iPod, Bluetooth, and E39 M5 Tire Pressure Monitor System

Re: The idle surge could be ICV if dirty...

... hate to be arrogant but in spite correct voltages to possible be right but ohms law is unforgivable because even a dirty ICV does open encloses throwing correct voltages, and there is bit more electronics that communicate failure to each other and corrupted codes too. However, the point is simple... and may have forgot to look under-the-hood... includes every coil, both CPS [cam and crank-shaft] sensors... fuel pressure regulator, fuel injectors... and down stream are O2 sensors. BTW, electronic either digital or analog communicate with each other... and failure of one affects the performance... so, good luck trouble-shooting the root of the problem...

Re: Find some Indy with an Autologic unit or a Dealer.

(hate not having a job ...)

Trying to diagnose this w/o paying a stealer ....

Have another issue going on, maybe related - leading to the question: "do you know what events cause the DME to go into 'limp-home'; are you familiar with what limp-home is like; do the E38 8-cyl have limp-home, or is that only for the V12's?"

Car has been at times going into a terrible rough idle with almost no power. Have to 'pump' the accelerator to get going like in the old carb cars.

SURPRISINGLY - when I pull the connector from the DME for a few minutes, the problem goes away. Returns after a while.

Does this sound like 'limp=home' - what events can cause such a thing? The only error code I have been getting (from stomp test) is a bad O2 sensor.

“limp home” gives you a specific cluster error…

There is a special “limp home” mode that can occur when certion sensors or components signal errors. This is called “Engine Failsafe Mode,” and you will always get an “ENGINE FAIL SAFE” message on the instrument cluster when that happens.

The symptoms you describe sound like a bad catalytic converter. The O2 sensor error is telling you that something is not right with one of the cats. That, combined with the severe misfiring is a signal that one of the cats is likely clogged.

At a minimum, you will need to get the engine diagnostics codes read by a BMW-specific tool like a Peake code reader. This should tell you the misfire errors and other cat-related errors. If you have a bad cat, then there is no point trying to sort out a MAF. You will need to deal with the cat problem first, and then go from there.

You are really at the point where will probably have to pay someone for some diagnostics time. The Stomp test does not give enough information to understand all that could be happening. Maybe someone nearby has a Peake code reader-- that will go a long way. However, you will probably have to connect to an Autologic or BMW computer.2000 E38 750iL Highline Edition with 18" Style 118 Wheels and Runflats
MKIV and 16:9 Navigation, TV, and Backup Camera
New Gen Radio, Sirius, Aux Input for my iPod, Bluetooth, and E39 M5 Tire Pressure Monitor System